Project Summary/Abstract Background: Low-income midlife and older adults are disproportionately impacted by a range of chronic diseases and conditions that contribute to widening US health disparities and can be alleviated by regular physical activity (PA), yet are among the most inactive segments of the US population. Relatively few PA programs have been developed specifically with their needs in mind, most of these interventions remain primarily at the individual level of impact, and few such interventions take full advantage of the recognized impacts that built and social environmental factors have for increasing and sustaining daily PA. Objective: The major objective of this application is to enhance the potential scalability and sustainability of person-level PA interventions by leveraging the capacity of residents themselves as local data gatherers and solution generators for neighborhood environmental change. The primary aim of the proposed group-randomized trial is to systematically compare the sustained (two-year) multi-level impacts of a lay advisor-delivered, person-level PA intervention that has demonstrated efficacy and translatability (Active Living Every Day) [ALED Alone arm], versus the ALED program in combination with a novel neighborhood-level intervention, called Our Voice [ALED+Our Voice arm]. The Our Voice program teaches residents to use a simple mobile application to individually and collectively identify neighborhood barriers to daily PA. They then convey this information to local stakeholders and decision-makers in ways that can facilitate potentially sustainable neighborhood-level improvements in support of regular PA. Design: We propose to randomize 16 public housing sites serving low- income, ethnically diverse midlife and older adults to ALED Alone vs. ALED+Our Voice (n=265 participants per arm; total=530). We hypothesize that 2-year ALED+Our Voice participant PA, measured via accelerometry, will be higher than in ALED Alone. We also will evaluate the 2-year impacts of the two programs on neighborhood- level PA using a standardized PA observation tool (SOPARC-path form). Additional questions of interest include levels of PA change at intermediate measurement time points; exploration of intervention effects in relation to a set of putative multi-level mediators; and exploration of the relative costs of the two interventions in relation to PA changes. We will also explore, in both arms, ongoing participant communication with local stakeholders (i.e., local organizations, media) that can set the stage for continued social and built environment changes beyond the project period. IMPACT: If the preliminary evidence supporting the promise of the Our Voice community engagement program is confirmed, it will provide a means for expanding the impacts and reach of person-level PA interventions beyond participants themselves to the neighborhood setting. This can, in turn, provide a scalable means for potentially sustainable PA promotion across broader income groups of relevance to US health disparities.